1. Field of the Invention
The invention relates generally to magnetic recording hard disk drives (HDDs), and more particularly to an HDD that optimizes the analog write current pulses in response to the frequency of the transitions in the data to be written to the disk.
2. Description of the Related Art
HDDs typically include a main integrated circuit, which is typically a system-on-a-chip (SOC) that contains many of the electronics and firmware for the HDD. The SOC receives the digital data to be written to the disk and transfers it to the read pre-amplifier/write driver integrated circuit (preamp IC). The preamp IC is typically located on the arm of the actuator that moves the read/write heads to the selected data tracks on the disks. The data to be written by the write head is sent from the SOC to the preamp IC, where the write driver generates analog write current pulses that are applied to the inductive coil in the write head to write data by selectively magnetizing the magnetic media of the recording layer on the disk. Registers in the preamp IC can be set to adjust the baseline write current magnitude (Iw) and the overshoot amplitude (OSA) of the write pulses.
Certain data bit patterns present difficulties for generation of the proper write current pulses. Closely-spaced transitions, such as transitions in consecutive clock cycles, require a larger-than-nominal OSA to generate adequate flux to saturate the media. Data patterns with long sequences of non-transitions (consecutive data 0's or consecutive data 1's) require a smaller-than-nominal OSA to prevent or minimize far track erasure (FTE). FTE arises because the write field from the write head is wider than a data track so when the write head is writing to a track, the outer portions of the write field (called the fringe field) overlap onto tracks other than the track being written. Data degradation due to fringe fields can extend over a range of tracks relatively far from the track being written. FTE is most likely due to domain walls that form in the magnetic shields and return pole of the write head. It has been determined that FTE is introduced if the OSA is too large for long sequences of non-transitions. FIG. 1 is a schematic illustrating FTE.
What is needed is a HDD with a write driver that can generate various levels of OSA to optimize the write current pulses for closely-spaced transitions and long sequences of non-transitions.